Role of electron temperature at extremely low density in negative positive ion plasma

It is pointed out that the role of electrons in dynamics pair ion and negative positive plasmas cannot be neglected even at extremely low density electrons, i.e., ne0n+0≪mem+ (where nj0 background jth species mj mass particles j-species while j = e, +, −) because electron thermal velocity almost always larger than velocities ions, vT± ≪ vTe. An analysis electrostatic waves unmagnetized (NPIE) (PIE) presented for case ωpe ωp+ ωpj=(4πnj0e2mj)1/2 plasma oscillation frequency corresponding to j-species). The contribute perturbations time scale longer wavelengths λDe2k2<1 where λDe=(Te4πne0)1/2 Debye length. On other hand, wave turns into when conditions ωp± 1≪λDe2k2 hold simultaneously acoustic approaches sum frequencies ions. only normal mode such a wavelengths, which also includes contribution electrons. separated from oscillations disappears with respect perturbations. Similar situation occurs having negatively charged dust particles. To elaborate these points, analytical results are applied two experiments NPIE PIE plasmas.